1. Field of the Invention
The present invention relates to a printer for forming a phase change inkjet image on a print substrate. The present invention further relates to a method for forming a phase change inkjet image on a print substrate.
2. Description of Background Art
A known inkjet printing apparatus for forming a phase change inkjet image on a print substrate comprises a print station and a sheet transport unit for advancing the sheet along said print station. The print station comprises a print head assembly for forming the phase change inkjet image. Said sheet transport unit comprises a sheet support platen and a feed mechanism for feeding the print substrate along the sheet support platen. The sheet support platen comprises a print surface for supporting a contact side of the print substrate. The print surface comprises a plurality of suction holes, which are arranged in fluid communication to a suction source for attracting the print substrate to the print surface.
The feed mechanism, such as a feed nip, is adapted for moving the print substrate in a transport direction over the print surface. The feed mechanism is arranged upstream of the print surface in the transport direction.
The print head assembly may be supported on a carriage, which is movably arranged for moving the print head assembly in a print swath over the print surface in a direction perpendicular to the transport direction. The feed mechanism may be controlled for intermittently advancing the print substrate over the print surface in between successive print swaths. The print substrate is attracted to the print surface by a suction pressure, which is continuously provided through the suction holes of the print surface.
The print head assembly is arranged for providing fluid ink droplets of an ink at a first temperature above room temperature for forming the phase change inkjet image in a print area on a process side of the print substrate, the process side being opposite to the contact side. The ink is solid or semi-solid at room temperature, such as a hotmelt ink, and the ink must be heated above its phase change temperature, such as its melting point, before droplets of liquid ink can be jetted onto the print substrate. The fluid ink droplets cool down upon application on the print substrate to a second temperature below the first temperature, thereby obtaining a phase change, such as a crystallization phase change transition. The rate of cooling down of the ink droplets on the print substrate may control the crystal sizes, which are attained during the crystallization phase change transition.
Some print substrates, such as films having a smooth surface, being advanced over the print surface have a problem of temporarily sticking to the print surface, thereby either slipping and/or bulging from the print surface. On the other hand, in case of lowering the suction pressure to reduce the sticking behavior on the print surface, the print substrate may be supported loose on the print surface. As a result, the temperature of the print substrate when supported on the print surface may not be accurately controlled and the crystallization of the ink on the print substrate may become disturbed leading to irregular crystals patterns, such as having both larger and smaller crystals, in the phase change inkjet image.